# std::tuple

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Defined in header `<tuple>` |  |
template< class... Types > class tuple; |  | (since C++11)

Class template `std::tuple` is a fixed-size collection of heterogeneous values. It is a generalization of std::pair.

If std::is_trivially_destructible<Ti>::value is true for every `Ti` in `Types`, the destructor of `std::tuple` is trivial.

If a program declares an explicit or partial specialization of `std::tuple`, the program is ill-formed, no diagnostic required.

### Template parameters

Types... | - | the types of the elements that the tuple stores. Empty list is supported.

### Member functions

(constructor) | constructs a new `tuple` (public member function)
operator= | assigns the contents of one `tuple` to another (public member function)
swap | swaps the contents of two `tuple`s (public member function)

### Non-member functions

make_tuple (C++11) | creates a `tuple` object of the type defined by the argument types (function template)
tie (C++11) | creates a tuple of lvalue references or unpacks a tuple into individual objects (function template)
forward_as_tuple (C++11) | creates a `tuple` of forwarding references (function template)
tuple_cat (C++11) | creates a `tuple` by concatenating any number of tuples (function template)
get(std::tuple) (C++11) | tuple accesses specified element (function template)
operator==operator!=operator<operator<=operator>operator>=operator<=> (removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(C++20) | lexicographically compares the values in the tuple (function template)
std::swap(std::tuple) (C++11) | specializes the std::swap algorithm (function template)

### Helper concepts

tuple-likepair-like (C++23) | specifies that a type implemented the tuple protocol (`std::get`, `std::tuple_element`, `std::tuple_size`) (exposition-only concept*)

### Helper classes

std::tuple_size<std::tuple> (C++11) | obtains the size of a `tuple` (class template specialization)
std::tuple_element<std::tuple> (C++11) | obtains the type of the specified element (class template specialization)
std::uses_allocator<std::tuple> (C++11) | specializes the std::uses_allocator type trait (class template specialization)
std::basic_common_reference<tuple-like> (C++23) | determines the common reference type of a `tuple` and a `tuple-like` type (class template specialization)
std::common_type<tuple-like> (C++23) | determines the common type of a `tuple` and a `tuple-like` type (class template specialization)
std::formatter<std::tuple> (C++23) | formatting support for `tuple` (class template specialization)
ignore (C++11) | placeholder to skip an element when unpacking a `tuple` using `tie` (constant)

### Helper specializations

template< class... Ts > constexpr bool enable_nonlocking_formatter_optimization<std::tuple<Ts...>> = (enable_nonlocking_formatter_optimization<Ts> && ...); |  | (since C++23)

This specialization of `std::enable_nonlocking_formatter_optimization` enables efficient implementation of `std::print` and `std::println` for printing a `tuple` object when each element type enables it.

### Deduction guides (since C++17)

### Notes

Since the "shape" of a tuple – its size, the types of its elements, and the ordering of those types – are part of its type signature, they must all be available at compile time and can only depend on other compile-time information. This means that many conditional operations on tuples – in particular, conditional prepend/append and filter – are only possible if the conditions can be evaluated at compile time. For example, given a std::tuple<int, double, int>, it is possible to filter on types – e.g. returning a std::tuple<int, int> – but not to filter on whether or not each element is positive (which would have a different type signature depending on runtime values of the tuple), unless all the elements were themselves constexpr.

As a workaround, one can work with tuples of std::optional, but there is still no way to adjust the size based on runtime information.

Until N4387 (applied as a defect report for C++11), a function could not return a tuple using copy-list-initialization:

    std::tuple<int, int> foo_tuple()
    {
        return {1, -1};  // Error until N4387
        return std::tuple<int, int>{1, -1}; // Always works
        return std::make_tuple(1, -1); // Always works
    }

### Example

Run this code

    #include <iostream>
    #include <stdexcept>
    #include <string>
    #include <tuple>

    std::tuple<double, char, std::string> get_student(int id)
    {
        switch (id)
        {
            case 0: return {3.8, 'A', "Lisa Simpson"};
            case 1: return {2.9, 'C', "Milhouse Van Houten"};
            case 2: return {1.7, 'D', "Ralph Wiggum"};
            case 3: return {0.6, 'F', "Bart Simpson"};
        }

        throw std::invalid_argument("id");
    }

    int main()
    {
        const auto student0 = get_student(0);
        std::cout << "ID: 0, "
                  << "GPA: " << std::get<0>(student0) << ", "
                  << "grade: " << std::get<1>(student0) << ", "
                  << "name: " << std::get<2>(student0) << '\n';

        const auto student1 = get_student(1);
        std::cout << "ID: 1, "
                  << "GPA: " << std::get<double>(student1) << ", "
                  << "grade: " << std::get<char>(student1) << ", "
                  << "name: " << std::get<std::string>(student1) << '\n';

        double gpa2;
        char grade2;
        std::string name2;
        std::tie(gpa2, grade2, name2) = get_student(2);
        std::cout << "ID: 2, "
                  << "GPA: " << gpa2 << ", "
                  << "grade: " << grade2 << ", "
                  << "name: " << name2 << '\n';

        // C++17 structured binding:
        const auto [gpa3, grade3, name3] = get_student(3);
        std::cout << "ID: 3, "
                  << "GPA: " << gpa3 << ", "
                  << "grade: " << grade3 << ", "
                  << "name: " << name3 << '\n';
    }

Output:

    ID: 0, GPA: 3.8, grade: A, name: Lisa Simpson
    ID: 1, GPA: 2.9, grade: C, name: Milhouse Van Houten
    ID: 2, GPA: 1.7, grade: D, name: Ralph Wiggum
    ID: 3, GPA: 0.6, grade: F, name: Bart Simpson

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 2796 | C++11 | triviality of the destructor of `std::tuple` was unspecified | specified
LWG 3990 | C++11 | a program could declare an explicit or partial specialization of `std::tuple` | the program is ill-formed in this case (no diagnostic required)

### References

- C++23 standard (ISO/IEC 14882:2024):

  - 22.4 Tuples [tuple]

- C++20 standard (ISO/IEC 14882:2020):

  - 20.5 Tuples [tuple]

- C++17 standard (ISO/IEC 14882:2017):

  - 23.5 Tuples [tuple]

- C++14 standard (ISO/IEC 14882:2014):

  - 20.4 Tuples [tuple]

- C++11 standard (ISO/IEC 14882:2011):

  - 20.4 Tuples [tuple]

### See also

pair | implements binary tuple, i.e. a pair of values (class template)

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